The long-term objective of this research proposal is to understand the role of anatomical and mechanical variables of the esophagogastric junction (EGJ) in the pathogenesis of gastroesophageal reflux disease (GERD). The candidate is currently in the first year of a tenure track faculty appointment in the Division of Gastroenterology and Hepatology at Northwestern University Medical School. He is seeking support for full time mentored research. His mentor, Dr. Peter Kahrilas is an NIH funded internationally-recognized expert on esophageal physiology and division head in the department of Gastroenterology and Hepatology. In addition, the candidate will be enrolled in the K30 sponsored Master of Science in Clinical Investigation Program at the Graduate School of Northwestern University. The proposed research study is to define the anatomical and mechanical variables of the EGJ as they relate to GERD. The EGJ is a complex anatomic zone whose functional integrity is sum of its many parts. To date, much of the research on the competence of the EGJ in GERD has been focused on the lower esophageal sphincter. Our hypothesis is that acquired anatomic changes inclusive of, but not restricted to hiatal hernia may alter the mechanical characteristics of the EGJ and affect the propensity to reflux. One such variable that will be studied is compliance. Increased compliance may exacerbate reflux in two ways: 1) lowering the incremental increase in intra-abdominal pressure required to open the relaxed or hypotensive EGJ, and 2) the relaxed EGJ may open wider than normal under a given physiological circumstance resulting in a reduced discriminative resistance for liquid as opposed to gas reflux. Compliance will be determined using a customized barostat technique and then correlated with hiatal hernia size, intra-abdominal LES length, angle of His and gastroesophageal flap valve grade. In addition, we will be attempting to improve standard pH monitoring technique by measuring acid exposure at the SCJ and converting data to hydrogen ion concentration exposure. These changes will improve diagnostic accuracy of pH monitoring and also help determine the relationship between anatomical and mechanical variants and acid reflux.